THE PEOBLEM OF MITOSIS. 
587 
bivalent chromosomes into a compact group at the equator ; 
that the membrane never breaks down, but envelops each 
chromosome in the metaphase and anaphase ; and lastly, that 
the spindle-cones are fibrils drawn out from the cytoplasmic 
reticulum by the receding membrane, and attached at one 
extremity to the chromosome envelopes. He concludes from 
these data that the cones are a visible expression of tension, 
and believes that the divergence of cone apices merely repre- 
sents transference of tension from one locality to another and 
is unaccompanied by movement of the fibres themselves. 
His first two assertions, which are the result of direct obser- 
vation, constitute a simple and efficacious method of collecting 
the scattered chromosomes into one spot before division, and 
may be the correct explanation of this phenomenon. His 
next assertion, however, is entirely hypothetical. Firstly, he 
asks us to believe in the existence of a membrane at a time 
when he himself says that it is invisible. Secondly, his 
drawings are inconclusive. He ,says that fig. 22, pi. 48, 
shows the beginning of envelopment of individual chromo- 
somes by the membrane : but in this figure I see only a slightly 
lobulate appearance of the nucleus such as is often observed 
ill somatic and spermatogonial resting stages. His fourth 
assertion is equivalent to saying that the spindle-cones are 
composed of mantle fibres ; for he affirms that the fibres are 
attached at one extremity to the chromosome envelopes. But, 
since the belief in the existence of these envelopes rests upon 
no evidence, this assertion also must be regarded as hy)) 0 - 
thetical. 
Before, however, passing on, let us suppose that his data 
are correct, and ask how far his conclusions, which concern 
only mantle fibres, affect spindle interpretation in other 
types. In the animal kingdom we find asters and a primary 
spindle, upon which the chromosomes later become arranged 
and divide : the presence of this spindle can no longer be 
denied ; for considerable controversy has recently taken place 
concerning it, and Gallardo himself has now been forced to 
admit its existence. If we turn to Meves’ paper upon the 
